1. Field of Invention
The present invention relates to a wrench and, more particularly, to a wrench equipped with a precise torque-measuring device.
2. Related Prior Art
As disclosed in U.S. Pat. No. 4,870,879, a wrench includes a ratchet arm 1, a shank 3, a torque assembly 2 arranged between the ratchet arm 1 and the shank, a handle 40 connected to the shank, and a dial 41 connected to the torque assembly 2. The dial 41 is allowed to spin relative to the handle 40. The dial 41 includes a scale 411. The handle 40 includes a pointer 401. The dial 41 is spun to set a maximum value of torque that can be transmitted to the ratchet arm 1 from the shank 3 and the handle 40 via the torque assembly 2. The pointer 401 and the scale 411 are used to show the maximum value of torque. The scale is based on N-m, lb-ft or kg-m. The scale 411 however cannot show the maximum value of torque precisely.
Such wrenches can be found in U.S. Pat. Nos. 2,205,510, 4,248,107, 7,044,036, 7,631,583 and D257626 for example. These wrenches cannot show the maximum value of torque precisely for reasons. At first, it is difficult to align the scale 411 to the pointer 401 precisely. Secondly, the precision in setting a digit in the ten's or hundred's place of a value of torque is acceptable; however, the precision in setting a digit in the unit's place of the value of torque is poor. This problem is particularly serious with U.S. Pat. No. 7,631,583 wherein the set value of the maximum value of torque must be compared with that is measured with an electronic measurement device. Thirdly, several dials are operated to set the maximum value of torque as disclosed in U.S. Pat. No. 7,631,583, and this is inconvenient.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.